Receiving serial data from a source is normally performed by shifting pulses across a medium from one location to another. This medium can be electrical wire or Radio Frequency (RF) signals. When data is received at its destination, the clock and data must be recovered.
One technology area holding much promise for the future of data transmission is the emerging Radio Frequency Identification (RFID) technology. RFID technology employs an RF wireless link and ultra-small embedded computer chips. RFID technology enables such things as allowing physical objects to be identified and tracked via wireless “tags”.
RFID systems, and particularly tags, are designed to operate on minimal power. Passive tags rely on the RF carrier signal for energy. The farther a passive tag is from the source of the carrier signal, the less power is generated. Accordingly, the range of a passive tag from the source of the carrier signal varies as a function of the power requirements of the tag.
Battery powered tags are constrained by a finite battery life, which in turn depends on power consumption. To extend the battery life, portions of active tags are typically powered down during a hibernate period. Upon receiving an activation signal, unpowered portions of the battery powered tag are activated. Thus, power consumption is critical in battery powered tags since any clock recovery circuit at the front end of a serial data input retrieval consumes power as it continuously samples the incoming signal for an activation signal.
Thus, in a low power tag, data signals must be decoded and recovered with minimum power. Current RFID clock recovery circuits use a Phase Locked Loop/Clock Data Recovery (PLL/CDR) circuit to recover the clock from an incoming data stream. One major problem is that the PLL circuit takes a long time to lock and consumes significant area and power, which is undesirable for RFID tags. The lock time can be reduced but it can never approach 2-3 cycles of preamble because it works in a feedback loop. Another traditional method to recover data is to over-sample the data at a higher frequency than the incoming data. Both of these methods consume unacceptable amounts of power, making the methods detrimental for implementation in RFID tags and impractical for such things as remote sensing devices.
What is needed is a low power circuit and method for recovering and decoding an incoming data pattern without requiring an active clock signal. What is also needed is a low power circuit and method for recovering and decoding an activation pattern, indicating that the device (e.g., tag) is to go from the hibernate state to the active state.